The components of two enzyme systems which catalyze hydroxylation reactions will be purified and characterized; (a) in Pseudomonas oleovorans, rubredoxin, NADH-rubredoxin reductase, and the omega-hydroxylase; (b) in liver microsomes, cytochrome P-450 and NADPH-cytochrome P-450 reductase. The manner in which these proteins serve as electron carriers or oxygen-activating catalysts will be determined. Multiple forms of cytochrome P-450 have been found; these will be characterized by their molecular weight, immunological properties, and substrate specificity toward drugs, carcinogens, fatty acids, steroids, etc.